An arrangement of the kind described above is disclosed in United Kingdom Pat. No. 2,007,878. In this patent, a simple electrical transmission of the actuator drive is described which is simple in the sense that it is without a safety arrangement. No provision is made for a defect in the drive arrangement so that the engine can die which is associated with a failure of power-assisted equipment such as self-energizing brakes, power steering and the like which makes the vehicle difficult to control.
On the other hand, an uncontrolled run up of the engine can occur. To prevent such problems, improvements have become known such as described in U.S. Pat. No. 4,494,517 wherein an actuator is disclosed which pivots to a defined opening cross section in the event of a failure of the drive. However, this solution too is not without problems since in the presence of different operating conditions such as temperature, air pressure and ancillary loads such as air conditioning, a fixed cross section cannot assure an idle operation for all conditions. Furthermore, United Kingdom Pat. No. 1,602,507 is representative of the state of the art wherein special drive motors are provided for actuators. In contrast, U.S. Pat. No. 4,356,802 discloses a special embodiment for actuators.